(1) Field of the Invention:
This invention relates to a guide rail for a passive seat belt system which is suitable for use in an automobile. The present invention is also concerned with a fabrication method of the guide rail.
(2) Description of the Related Art:
The use of a seat belt system has become popular in recent years, mainly, due to the mandatory requirement for the use of a seat belt system for an automobile occupant. In order to avoid the rather cumbersome fastening and release of its webbing, there is an increasing demand for passive seat belt systems which permit automatic fastening or release of a webbing in accordance with the opening or closure of an associated door.
In order to facilitate the understanding of the present invention, one example of general passive seat belt systems is described first of all with reference to FIG. 12 which illustrates the overall construction of the exemplary passive seat belt system. Numeral 10 indicates a stationary base of an automobile, while numeral 20 designates a seat. The drawing also shows a webbing 1, a retractor 2 fixed on the seat 20 and adapted to take up or pay out the webbing 1, and an emergency release buckle (hereinafter referred to simply as "buckle") 3 which permits the release of the webbing 1 upon depression of a release button or the like in the event of an emergency. A tongue 21 fastened to the outboard end of the webbing 1 is inserted in the buckle 3. Designated at numeral 4 is a movable anchor which is integral with the buckle 3. The movable anchor 4 travels, together with the buckle 3, through a rail 6 between an anchor base 5 arranged behind the seat 20 and the front end of the rail 6. In order to control the movement of the movable anchor 4, a front end switch 7 and an unillustrated rear end switch are provided at the front end of the rail 6 and within the anchor base 5 respectively. Designated at numeral 22 are brackets by which the rail 6 is mounted on the stationary base 10. Numeral 8 indicates a drive member, such as wire, for driving the movable anchor 4, while numeral 9 designates a drive unit for taking up or pushing out the drive member 8. The operations of the drive member and drive unit are well known in the art and their descriptions are omitted herein.
When the door is opened, the drive member 8 is pushed out from the drive unit 9 so that the movable anchor 4 is guided toward the front of the vehicle along the rail 6. As soon as the movable anchor 4 is brought into contact with the front end switch 7, the switch 7 stops the operation of the drive unit 9. Since the buckle 3 fixed on the movable anchor 4 has been brought to a front part of the stationary base, the webbing 1 is apart frontward from an occupant (not shown) so that the occupant is allowed to get off or get on the automobile easily.
When the occupant then gets on the automobile and closes the door, the drive unit 9 is actuated to take up the drive member 8, whereby the movable anchor 4 is then guided back to the anchor base 5 along the rail 6. Owing to the provision of the unillustrated rear end switch within the anchor base 5 as mentioned above, the operation of the drive unit 9 is stopped upon arrival of the movable anchor 4 at the anchor base 5. As a result, the webbing 1 restrains the body of the occupant as depicted in FIG. 12.
FIG. 13 is a cross-sectional view of the rail 6 taken along line XIII--XIII of FIG. 12, in which there are illustrated a second guide channel 61 for the drive member 8, a first guide channel 62 for the movable anchor 4, a strait portion 63, and an opening 64. FIG. 14 shows by way of example one method for forming a rail stock 6', whose cross-sectional shape is depicted in FIG. 13, into a desired shape. The stock 6' is pressed against a bender 70 by applying forces in directions M,M, whereby the stock 6' is bent and finished into a rail of a three-dimensional complex curvilinear configuration conforming with a corresponding inner wall portion of the stationary base. FIG. 15 is a cross-sectional view taken along line XV--XV of FIG. 14. The bender 70 has side walls 71,73 and central wall 72, so that the rail stock 6' is fittingly received in the bender 70. This structure of the bender 70 is used, because both side walls of the rail stock 6' have to be supported by walls B',C' in order to prevent the rail stock 6' from being deformed in transverse directions indicated by arrows B,C respectively.
As illustrated in FIGS. 13-15, conventional rails are each fabricated by extruding aluminum into the rail stock 6', which defines the opening 64, both guide channels 61,62 and strait 63, and then bending the rail stock 6' three-dimensionally. In view of the function assigned to these conventional rails, they cannot perform as designed unless their transverse cross-sectional configurations are finished with good dimensional accuracy. Their shapes may be deformed unless they are bent by holding or supporting them at portions as many as possible on a bender. Although it is also desirous to support the inner walls of a rail at portions as many as possible on the bender, undercut portions D do not allow the bender to support the rail there. Accordingly, the rail is not supported at the undercut portions D. The undercut portions D therefore cause deformations. For example, the bending may cause a reduction in the width of the channel 61 or 62 at one or more longitudinal sections of the rail.